The use of electric belly-band heaters is well known in the prior art. Typically, these heaters use resistance heating wherein a resistance heating wire or heater cable is encased in a metal sheath. The metal sheath is in contact with the item or material to be heated. One type of belly-band heater (commonly referred to as a “crankcase heater”, “compressor heater” or “sump heater”) is used to heat refrigeration compressors or air-conditioning compressors. The heater can employ a standard hose clamp or other type of clamping arrangement for attachment to the compressor. The standard hose clamp is cut in two pieces with each piece affixed (welded for example) to opposite ends of the heater's metal sheath. Assembly of the heater to the compressor is accomplished by engaging the two ends of the clamp as intended and then tightening the assembly around the selected compressor location. This type of heater construction can also be used for heating containers such as barrels, heating pipes, etc.
The belly-band heater has an insulated electric lead wire exiting each end of the metal sheath. A frequent requirement in the use of these heaters is for the lead wires to be routed in standard metal conduit. Further, it is often required that the conduit enclose the lead wires from the point where each lead exits the heater sheath to where the lead wires enter an electrical junction box or boxes.
FIG. 1 shows a typical metal sheathed heater or electric belly-band heater designated by the reference numeral 10 and including the hose clamp pieces 1 and 3, and the screw mechanism 5. A metal sheath 7 extends between the two pieces 1 and 3, with the hose clamp pieces attached to the sheath by welding or the like. The metal sheath 7 encases an electrically insulated resistance heating wire or heater cable 9 and includes a fluted strip portion 8, which interfaces with the equipment or material requiring heating and is more fully explained below.
In these types of metal sheathed heaters, it is well known in the industry that the heater cable is composed of resistance wire spiraled around a flexible core made of an electrically insulated and thermally resistant material such as fiberglass or other suitable material. This element is commonly referred to as a “heater core wire”. After the heater core wire is uniformly coated with an insulating material having sufficient mechanical and electrical resistance properties so as to remain flexible yet electrically isolated, it is normally called a “heater cable”. The insulating material is often silicone or a thermosetting plastic with adequate thermal properties for its intended use.
A small length of insulation is stripped from each end of the heater cable. Two flexible electrically insulated stranded lead wires with a small length of insulation stripped from one end of each wire are electrically connected, one to each end of the heater cable, by crimping or splicing the stripped ends of the heater cable to stripped ends of the lead wires. The connector used is a properly selected metal splice connector with sufficient temperature resistance, corrosion resistance, mechanical strength and formability to make a secure electrical bond.
In the prior art, a suitable material is molded around each metal splice joint to electrically isolate the metal connectors. The molding material is a substance which bonds with both the insulation of the heater cable and the insulation of the lead wire. The heater cable-lead wire combination, with molded insulation around the splice as described, is normally referred to as a “heater cable assembly”. The heater cable assembly is enclosed in the metal sheath 7, see FIG. 1, which is commonly in the form of a tube, open at each end and of length sufficient to cover the heater core wire along its entire length. Generally the greater portion of the length of the two lead wires extends beyond the metal sheath to reach terminals so electrical power may be connected to each lead wire for activating the heater.
One version of a prior art metal sheathed heater is a Model CH made by TUTCO, Inc. of Cookeville, Tenn., see FIG. 1 again. The heater 10 is typically wrapped around and clamped in place on the outside of an air conditioning or refrigeration compressor to heat a substance such as compressor oil. While a hose clamp is illustrated, any type of attachment can be employed to secure the metal sheathed heater to the component desired to be heated. These arrangements are well known and do not need further description for understanding of the invention.
The heater cable 20, as shown in FIG. 2, is made with a heater core wire 21 having a fiberglass central core 23. The heater cable assembly 25 is made with the heater cable 20 and two stranded lead wires 26 and 28. At the splice, these components, all essentially having same outside diameter, see FIG. 3, are insulated with molded silicone 30, the mold matching the diameter of the wires and cable. The molding material used is silicone because this is the only known substance that will bond with the silicone used in the heater cable and lead wires and make an adequate terminal splice seal.
Presently, the requirement of encasing the lead wires in conduit is achieved by attaching specialized parts/items where the heater is being used so as to protect the lead wires and meet installation codes. This procedure is both time-consuming and costly. In conjunction with the special rigging required to meet the requirement of enclosing the lead wires at the heater itself, opposite ends of the conduit would also be attached to standard junction boxes or the like.
One of the problems with prior art heaters is the use of silicone wiring for the heater cable and lead wires. When silicone-insulated wires are manufactured, the wires are placed on take-up rolls during the wire production process. To prevent the silicone insulation on the wires from sticking during the take up roll process, a thin layer of powdered talc is applied to coat the wire surfaces. The talc must be removed from the splice section prior to a molding process as the talc will contaminate the cross section area of the cut surfaces formed during the insulation stripping process. The presence of talc prevents the silicone mold material from sticking to the cut cross section surfaces of the wire insulation.
During the process of stripping insulation from the ends of the wires and the process of connector splicing, it is possible for pieces of fiberglass to contaminate the area. Also, the ends of the resistance wire and/or the ends of the stranded lead wires may not be properly captured by the splice connector. An example of this is shown in FIG. 4 wherein a portion of the heater core wire 21 lies outside the connector 32. In order to detect and then correct the aforementioned conditions prior to molding, intense manual inspection is performed on each splice joint and rework is done as required, both assisted by visual magnification.
Referring to FIGS. 5a and 5b, the sheath 40 for the heater is made by a thin metal strip tightly wrapped around the periphery of the heater cable and cable assembly. The metal strip is slightly wider than the circumference of the heater cable and slightly longer than the heater cable which is centered along the sheath length. Each lead wire is of sufficient length to extend to electrical power terminals. Special “fingers” 41, all the same width, are stamped along each side and at a direction perpendicular to the centerline of the length of the strip. Spaces 43 between the strips are created and the fingers 41 are of the same dimension. The strip is initially made in a flat form, see FIG. 5a, and is preformed into a “U” cross section 45, see FIG. 5b, prior to the operation of wrapping the metal strip around the heater cable assembly. The “fingers” 41 on one side of the strip are offset when compared to those on the opposite side so all will interlock once the strip is formed into its intended final shape, see FIG. 1. Each space is slightly wider than the width of each “finger” to create a loosely interlocked condition after the metal strip is wrapped around the heater cable assembly. Finally and as shown in FIG. 1, a two-piece metal clamp arrangement is welded to the formed metal sheath, one piece to each end of the sheath, and the entire heater assembly is formed to fit the shape of the compressor for which it was designed. Referring to FIG. 1, it can be seen how the “fingers” loosely interlock and contact the compressor body to enhance heat transfer.
Referring again to FIG. 3, the mold covering 30 of the splice connector section 25 is designed to be at the same outside diameter as the two adjacent wires 20 and 26 connected by the splice. This ensures sufficient insulation between the metal connector and the metal sheath. Also, if the mold section is at a diameter larger than that of the wires, the mold section 30 can or will be cut when the metal sheath is formed around the assembly resulting in either improper heater operation or failure. There must be no breaks, cracks or any path whereby current can leak to the metal sheath, either from the live electric splice connectors or from the live resistance wires of the heater cable immediately adjacent to the splice section. Such a flaw can result in either improper operation or failure of the heater.
For the TUTCO, Inc. model CH compressor heaters, secure mold sections on each heater built are essential for proper operation. However and during the manufacture of these CH model heaters, a number of hard to identify conditions can occur that, if are not detected prior to using, the heater can fail. These conditions could be breaks, cracks or incomplete bonding between the wire insulation and the mold material resulting in heater failure. Also, should either the end of a heater core wire or the end of a lead wire strand protrude outside the splice connector and extend a distance equal to or greater than the distance to the outer surface of the molded section, a direct electrical path to the metal heater sheath is created resulting in heater failure, (See FIG. 4). Further, if either a piece of fiberglass from the core wire or some of the powdered talc used to coat the silicone insulation becomes imbedded in the mold area, a defect can occur resulting in heater failure.
Another hard to identify defect is either very tiny holes or cuts in the heater cable adjacent to the mold sections that are not sealed by the molding silicone. The holes and cuts occur either when the wires are cut to length, insulation stripped from their ends or when the metal connector is spliced to the wires during the process of connecting the heater cable ends to the lead wire ends. These holes and cuts result when the tools used in performing these operations becomes worn or out of adjustment and impinge on the insulation covering the wires with sufficient force to cut through to the metal underneath.
It does not work to cover all the defect types mentioned above by making the mold section to a diameter larger than the wire diameter and extend it to cover any possible holes or cuts in the insulation as mentioned above. This is because molded sections, larger in diameter than the wires, will be cut and rendered defective when the metal sheath is applied as described above. The same is true if an insulating tube or tape is placed over the potentially defective area and the sheath closed as intended.
Another problem with the prior art is that it is not possible to use lead wires with insulation other than silicone because only silicone will bond to silicone. Other lead wires are available and made with insulating materials that are tougher than silicone, have temperature ratings high enough for heater lead wire applications and are less expensive than silicone. Often times, the ends of the formed sheath have sharp edges and when the heater is installed in its intended location it is possible for the soft silicone lead wire insulation to accidentally be forced against a sharp edge cutting deep enough to create a defect.
As a result of the problems encountered concerning the splice connection of the prior art metal sheathed heaters, a need exists to provide an improved splice connection. The present invention solves this need by providing a splice connection that eliminates the need for using a silicone molding compound and molding operation for the splice connection, and avoids many if not all of the problems noted above regarding the prior art metal sheathed heaters.